| Autor: |
O'Rourke, Laurence, Heinisch, Philip, Blum, Jürgen, Fornasier, Sonia, Filacchione, Gianrico, Van Hoang, Hong, Ciarniello, Mauro, Raponi, Andrea, Gundlach, Bastian, Blasco, Rafael Andrés, Grieger, Björn, Glassmeier, Karl-Heinz, Küppers, Michael, Rotundi, Alessandra, Groussin, Olivier, Bockelée-Morvan, Dominique, Auster, Hans-Ulrich, Oklay, Nilda, Paar, Gerhard, Perucha, Maria del Pilar Caballo |
| Zdroj: |
Nature; 10/29/2020, Vol. 586 Issue 7831, p697-701, 5p |
| Abstrakt: |
On 12 November 2014, the Philae lander descended towards comet 67P/Churyumov–Gerasimenko, bounced twice off the surface, then arrived under an overhanging cliff in the Abydos region. The landing process provided insights into the properties of a cometary nucleus1–3. Here we report an investigation of the previously undiscovered site of the second touchdown, where Philae spent almost two minutes of its cross-comet journey, producing four distinct surface contacts on two adjoining cometary boulders. It exposed primitive water ice—that is, water ice from the time of the comet's formation 4.5 billion years ago—in their interiors while travelling through a crevice between the boulders. Our multi-instrument observations made 19 months later found that this water ice, mixed with ubiquitous dark organic-rich material, has a local dust/ice mass ratio of 2.3 − 0.16 + 0.2 : 1 , matching values previously observed in freshly exposed water ice from outbursts4 and water ice in shadow5,6. At the end of the crevice, Philae made a 0.25-metre-deep impression in the boulder ice, providing in situ measurements confirming that primitive ice has a very low compressive strength (less than 12 pascals, softer than freshly fallen light snow) and allowing a key estimation to be made of the porosity (75 ± 7 per cent) of the boulders' icy interiors. Our results provide constraints for cometary landers seeking access to a volatile-rich ice sample. When the Philae lander bounced on the surface of comet 67P/Churyumov–Gerasimenko, it exposed primitive icy-dust material within cometary boulders; the intrinsic strength and porosity of this material is reported. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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